Right, and I believe it even works correctly now... The original API had the
update time information as part of the constructor, but I didn't see that as
the correct thing to do, but I also did not think to export it.
I am working on updating the QtGUI, hopefully to resolve the segmentation
fault issue when you close it. I'll wrap this function and export it so you
can use it later.

On further study, it appears the sink constantly does the fft
calculation and only updates the display periodically.

What would be helpful for me is only run the fft when you update the
display. Calculating the fft continuously is a waste of time. (Well, for
an fft you display)